1. Field of the Invention
Aspects of the present invention relate to a method of manufacturing a thin film transistor and a method of manufacturing an organic light emitting display having the thin film transistor, and more particularly to a method of manufacturing a thin film transistor having a compound semiconductor containing oxygen as a semiconductor layer and a method of manufacturing an organic light emitting display having the thin film transistor.
2. Description of the Related Art
Generally, a thin film transistor includes a semiconductor layer including a channel region and source and drain regions, and a gate electrode formed on the channel region and electrically insulated from the semiconductor layer by a gate insulating layer. The semiconductor layer of the thin film transistor configured as above is generally formed of amorphous silicon or poly-silicon. However, if the semiconductor layer is formed of amorphous silicon, charge mobility in the semiconductor layer is low and causes difficulties in implementing a driving circuit to be operated at high speeds. If the semiconductor is formed of the poly-silicon, charge mobility in the semiconductor layer is high whereas threshold voltage in the semiconductor layer becomes uneven and results in additional use of a separate compensation circuit.
Also, a method of manufacturing a typical thin film transistor using low temperature poly-silicon (LTPS) involves high-cost processes such as laser annealing, etc., and control of its property is difficult, and leads to a difficulty in applying the technique to a large area substrate.
In view of the above problems, a study is under way to use the compound semiconductor as the semiconductor layer. Japanese Patent Publication No. 2004-273614 discloses a thin film transistor using zinc oxide (ZnO) or a compound semiconductor using zinc oxide (ZnO) as a main ingredient as the semiconductor layer.
However, if the compound semiconductor is used as the semiconductor layer, a problem arises in that conductivity is reduced due to infiltration of hydrogen (H) when exposed to air. The hydrogen infiltrated into a surface part of the compound semiconductor layer acts as a shallow donor to reduce the conductivity of the semiconductor layer, and such a reduction of the conductivity intensifies according to the exposed time thereof. Therefore, owing to the reduction of the conductivity on the channel region, the electrical property of the thin film transistor is deteriorates, thereby leading to an increase in a leakage current, etc.
Regarding the reduction of the conductivity of the semiconductor layer due to infiltration of hydrogen, a thesis titled, “Role of Intentionally Incorporated Hydrogen I Wide-Band-Gap ZnO Thin Film Prepared by Photo-MOCVD Technique”, cP772, Physics of Semiconductors; 27th International Conference on the Physics of Semiconductors may be referred to.